Ceramic dielectric block filters offer several advantages over air-dielectric cavity filters. The blocks are relatively easy to manufacture, rugged, and relatively compact. In the basic ceramic block filter design, resonators are formed by cylindrical passages called through-holes which extend between opposed top and bottom surfaces of the block. The block is substantially plated with a conductive material (i.e., metallized) on all but one of its six (outer) sides and on the interior walls of the resonator through-holes.
The top surface is not fully metallized but instead bears a metallization pattern designed to couple input and output signals through the series of resonators. In some designs, the pattern may extend to the sides of the block, where input/output electrodes or pads are formed.
The reactive coupling between adjacent resonators is dictated, at least to some extent, by the physical dimensions of each resonator, by the orientation of each resonator with respect to the other resonators, and by aspects of the top surface metallization pattern.
Although such RF signal filters have received widespread commercial acceptance since the 1970s, efforts at improvement on this basic design have continued to the present.
For example, there continues to exist a need to increase power-handling capabilities of ceramic filters for higher power applications. Currently, increasing the ceramic body size and/or the top pattern gaps to their maximum is the primary method used to increase the power handling capability of monoblock filters. Increasing the gaps in some cases, however, reduces the electrical performance of the filter and creates manufacturing sensitivity issues. Moreover, and where size and space is a limitation, increasing the size of the ceramic body is not an option.
Therefore, the need continues for an improved RF monoblock filter which can offer improved and increased power handling capabilities without either an increase in the size of the filter or an increase in the size of the gaps in the top metallization pattern.